1. Field of the Invention
This invention relates to a preform for making a plastic can body without a cutting process and to a method of manufacturing a plastic can body by using such preform.
2. Description of the Related Art
Fluids such as drink and oil have been usually held in iron or aluminum cans up to now. With a wide use of plastic bottles in place of glass bottles, there is a large demand to hold such fluid in can-like plastic containers.
Examples of such containers are disclosed in Japanese Patent Publication Sho-58 501991, and Japanese Patent Laid-Open Publications Sho-60 25734 and Sho-60 72720.
With these conventional examples, a preform is made by the injection molding process, then being subject to the biaxial stretch blow molding process to form a container having a flange around its top. The container is cut at an unnecessary portion of the flange by a cutter. The flange serves to double seam a lid.
The blow-stretched flange is small in thickness but has a sufficient mechanical strength due to the orientation of the plastic material, and also has properties to prevent permeation of gas into the container. Since such a blow-stretched flange is formed as part of a side wall of the container, it is inevitable to cut an unnecessary portion of the flange by a cutter or the like. The cut edge of the flange may be nicked. Even if the flange is formed by the biaxial stretch blow molding process to have the stretching orientation, extensive stress will be applied to the cut edge of such flange, which would cause cracks in the cut edge, reduce the mechanical strength and durability when the flange is curled and double-seamed with the lid.
Forming the flange by the stretch blow molding process largely depends upon conditions such as material and molding process. Therefore, it is very difficult to produce the flange having a uniform thickness. Sometimes, the flange has a different thickness in its circumferential direction.
In the foregoing methods, the cutting process not only complicates the container manufacturing process but also makes the flange less reliable in its dimensions and durability.